1. Field of the Invention
The present invention relates to an origin detector for a lamp unit in an image scanner.
2. Description of the Related Art
The image scanner needs an origin (reference position) for a lamp unit to hold a reading start position. Thus conventional image scanners use a photosensor, a reed switch, or the like to detect a reference position. In the arrangement of a conventional image sensor in FIG. 3B, an output signal from a sensor 1 is linked with an interrupt terminal 2 also serving as an I/O port of a CPU 3, which performs interrupt operation by detecting the timing of turn-on and turn-off of the sensor at a rising edge and a falling edge.
Referring now to FIG. 5C, the arrangement of a conventional scanner is described below. Numeral 7 indicates a lamp unit, which is arranged to be moved along a shaft 12 by a motor 11. Numeral 6 designates a home position sensor for detecting an origin for the lamp unit. Numerals 8, 9, and 10 indicate a mirror unit, a CCD for reading an image, and a lens, respectively. Numerals 13 and 14 designate belts, and numerals 15 and 16 represent pulleys.
Referring now to the flowchart in FIG. 2 and the arrangement of the scanner in FIGS. 5C and 5D, a conventional controlling method using a sensor is described below.
Sensor condition is checked immediately after the power is turned on (S201). If the sensor is off (the lamp unit is not in the position of the sensor) as shown in FIG. 5C, the lamp unit moves back toward the sensor (S202 and S203) until the sensor turns on (the lamp unit is in the position of the sensor). After the sensor turns on, the lamp unit further moves back a few steps to make sure that the sensor is on (S204). Then the lamp unit begins to move forward (S205) and stops (S207) at such a position that the sensor turns off (S206), that is, an origin.
If the sensor is on as shown in FIG. 5D immediately after the power is turned on (S201), the lamp unit moves forward and stops at such a position that the sensor turns off, that is, an origin. This allows the previous operations (S202 to S204) to be omitted.
Such a position that the sensor is switched off is specified as an origin, since the range in which the sensor turns on cannot be neglected in relation with variations in the reading start position particularly if a reed switch is used.
A scanner using a conventional origin detector is disclosed in Japanese Patent Application Laying open (KOKAI) No. 4-329531.
Conventional origin detectors are expensive because they use a sensor. What is worse, conventional origin detectors need space for a sensor and cables, so that the detectors are prevented from being reduced in size. In addition, problems with assembly may arise because of installation variations. The present invention is made to solve the problems and provide an origin detector enabling a small inexpensive image scanner to be created.